The present invention relates to an actuator device comprising a flexible cable, having one end connected to a control member and a flexible sheath, in which the flexible cable is mounted, where at least one portion of the flexible cable is made of a shape-memory material, which is able to undergo a variation in shape following upon its being heated, in order to control the controlled member.
Flexible-cable actuator devices find application in a wide range of fields and in general wherever it is necessary to provide for simple and inexpensive mechanical transmission which will enable remote control of displacement of a member. Flexible-cable actuator devices are, for instance, used to enable manually controlled actuation in motor vehicles, for example for release, from inside the vehicle, of the hatchback door or the bonnet, or for operation of mobile parts or mechanisms for car-seat adjustment, or for operation of mobile members of the engine or facilities on board the vehicle.
A flexible-cable actuator device having the characteristics referred to at the beginning of the present description, is known from the document DE-C-199 16 244. This known device is designed always to be controlled manually. However, its operation causes an activation of the shape-memory element, with the consequence that the controlled member undergoes an additional displacement with respect to the displacement caused by mere manual operation.
Instead, the purpose of the present invention is to provide an actuator device of the type referred to at the beginning of the present description, which will be selectively usable as a manually controlled mechanical transmission, as well as just by electrical operation.
With a view to achieving the above purpose, the subject of the invention is an actuator device comprising:
a flexible cable, having one end connected to a controlled member; and
a flexible sheath within which the flexible cable is mounted;
in which at least one portion of the flexible cable is made of a shape-memory material, that is able to undergo a variation in shape following upon its being heated, so as to control the controlled member;
characterized in that the aforesaid sheath is mounted with respect to a fixed supporting structure, so as to be free to displace longitudinally only in a direction corresponding to the direction of operation of the controlled member; and
in that the aforesaid sheath is coupled to the controlled member, so as to be able to transmit to the latter a displacement in the aforesaid direction of operation and so as to be decoupled, instead, from the controlled member when there is a displacement in the opposite direction, in such a way that said actuator can be used both manually, as a mechanical-transmission element, using the sheath as transmission element, and by exploiting the variation in shape of the shape-memory cable induced by the fact of its being heated.
It is, in the first place, to be pointed out that the invention is of general application and can therefore also be used outside the automobile sector, and, in particular, in any sector in which it might prove useful to apply an actuator device that can be operated both manually and electrically.
Shape-memory actuator elements have been known for some time and used in a wide range of fields in which it is necessary to have available actuator means of simple structure and low cost. They use shape-memory metal alloys that can undergo deformation after a predetermined transition temperature is exceeded. In general, heating may be obtained in so far as the actuator element is able to detect directly a variable ambient temperature, or else by supplying an electrical current through the actuator element so as to heat it by the Joule effect. In this case, the electric-supply means may also be associated to electronic control means designed for controlling current supply on the basis of a signal detected by a temperature sensor, a position sensor or displacement sensor, or a potentiometer.
In the preferred embodiment of the present invention, electric-supply means are provided so that the flexible cable will be traversed by an electric current for it to be heated by the Joule effect above the transition temperature.
When the device is used as a simple mechanical-transmission element, it is sufficient to exert a tensile force on one end of the sheath for the said tensile force to be transmitted by the latter to the controlled member. In the alternative mode of operation, no tensile force is exerted on the device, and it is just necessary to enable supply of electric current through the flexible cable, so as to cause contraction by the shape-memory effect.
In a wide range of applications, associated to the controlled member are elastic means, which recall it towards a resting position. In many cases, such elastic means associated to the controlled member may be sufficient to ensure that the actuator device according to the present invention will return to its starting condition when the shape-memory flexible cable is cooled off to bring it back into its condition of greater length. In other applications, it may instead be advantageous to incorporate, in the aforesaid bushing, elastic means, designed for favouring return of the shape-memory element to its resting condition.